This invention relates to a process for the purification of 1,10-decanedicarboxylic acid.
1,10-Decanedicarboxylic acid (DDA) is a valuable starting compound for the production of polymers, such as polyamides and polyesters. A number of methods for the production of 1,10-decanedicarboxylic acid are known from the literature. Ordinarily, cyclododecanone or cyclododecanol or a mixture thereof is oxidized to 1,10-decanedicarboxylic acid by oxidation with nitric acid under mild conditions, usually in the presence of oxidation catalysts such as, for example, copper salts and vanadium salts.
Heretofore, great difficulties have been encountered in obtaining, in a simple manner, 1,10-decanedicarboxylic acid in the purity required, for example, when used as a polyamide or polyester component. It also has been especially difficult to produce 1,10-decanedicarboxylic acid with very low color numbers, i.e., in the so-called fiber quality.
According to German Pat. No. 737,691, it is practically impossible to purify longer-chain .alpha.,.omega.-dicarboxylic acids by distillation. It is indicated in French Pat. No. 1,393,569 that nitrogen-containing compounds are formed during the oxidation of cycloalkanols and cycloalkanones with nitric acid to obtain .alpha.,.omega.-dicarboxylic acids, and that these byproducts impair the thermal stability of the product. The aforementioned patent discloses that the dicarboxylic acids are obtained in a sufficiently pure form by recrystallization from organic solvents.
A number of literature references are known wherein the attempt is made to obtain very pure 1,10-decanedicarboxylic acid by recrystallization, melt crystallization, or similar methods. (See, for example, French Pat. No. 1,393,568; U.S. Pat. No.3,413,138; German Unexamined Laid-Open Application DOS No. 1,443,811; German Pat. No. 1,903,571; and DOS No. 2,101,942.) Thus, heretofore, it was necessary to employ complicated and expensive recrystallization processes to obtain 1,10-decanedicarboxylic acid of high purity.
It is an object of this invention to provide a method of purifying, by a simple method, 1,10-decanedicarboxylic acid produced by the nitric acid oxidation of cyclododecanol and/or cyclododecanone with nitric acid to such an extent that it can be used directly as a polyester or polyamide component.